Ovarian granulosa cells are essential for successful follicle development. Dysregulation of granulosa cell proliferation and differentiation may lead to impairment of female fertility or development of ovarian tumors. Although studies indicate that the Hippo signaling pathway plays critical roles in both development and tumorigenesis of several organs, its role in ovarian physiology and pathology remains largely unknown. The present study aims to investigate the role of YAP in ovarian granulosa cell proliferation, differentiation and transformation. Immunohistochemical analyses showed that the active form of YAP (nuclear YAP) was highly expressed in proliferative granulosa cells, whereas the inactive form of YAP (cytoplasmic YAP) was detected mainly in terminally-differentiated luteal cells, indicating that YAP may be involved in proliferation and differentiation of ovarian granulosa cells. Knockdown of YAP or pharmacological inhibition of YAP activity in human granulosa cells suppressed cell growth and reduced cell survival in both traditional 2D cell culture system and a novel 3D hanging-drop culture system, suggesting that YAP is essential for the growth and survival of human granulosa cells. In addition, ectopic expression of wild-type or constitutively active YAP impaired gonadotropin-induced differentiation of granulosa cells and stimulated the rapid growth and transformation of granulosa cells, findings which were reflected by increased colony formation in soft agar assay and growth of tumors in a xenograft mouse model. Injection of verteporfin (a selective antagonist of YAP) into female CD1 mice inhibited granulosa cell growth, induced GC apoptosis, and disrupted mouse ovarian follicle development, leading to severe subfertility. Consistently, mice with ovarian granulosa cell-specific expression of constitutively active YAP demonstrated disruption of granulosa cell differentiation and failure of ovarian follicle development. In conclusion, our studies demonstrate that homeostatic YAP expression and activation are essential for ovarian granulosa cell proliferation, differentiation and survival. YAP is a novel therapeutic target for treatment of ovarian diseases associated with granulosa cell dysregulation.
Citation Format: Xiangmin Lv, Chunbo He, Guohua Hua, Jixin Dong, John S. Davis, Cheng Wang. Yes-associated protein 1 (YAP) in the growth and tumorigenesis of ovarian granulosa cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A37.